This invention pertains to the art of electromagnetic devices and more particularly to electromagnetic devices useful for lifting a variety of magnetizable items such as iron or steel scrap and loose ferro-magnetic material. However, it will be appreciated by those skilled in the art that the invention could be readily adapted for use in other environments as, for example, where similar lifting devices are employed to lift or transport other types of materials.
A wide variety of electromagnetic lifting devices are known in the art. The lifting power of such devices depend upon the density of magnetic flux normal to the plane of engagement between the material to be lifted and the magnet. In addition, the lifting power varied directly as a square of the normal flux density. Therefore, most lifting electromagnets are designed to employ a conformation for securing a relatively high density and definitely directed flux pattern to achieve more economical operation. All electromagnets employ an electrical coil generating a toroidally directed flux pattern about the coil. As the flux pattern is more dense radially within the coil, as opposed to the density of the flux pattern radially outset from the coil, most conventional electromagnets include a specific lifting surface substantially within the diametrical area of the coil. See U.S. Pat. No. 794,086 to Eastwood. Such a lifting surface possesses generally normally directed flux lines.
The flux lines are initially communicated through a magnetic core positioned radially within the coil and, from the core, are further communicated along the outer periphery of the magnet through outer jackets of magnetic material. The communication of the flux lines through the jackets prevents magnetic attachment to the outer sides of the magnet as opposed to the lifting surface. The jackets are spaced and magnetically insulated from the lifting surface to cause the flux lines to radiate from the jackets through the ambient air to attract a lifted item towards the lifting surface. The lines then pass through the lifting surface and ultimately back to the core which is typically in magnetic engagement to the lifting surface.
Such conventional types of lifting electromagnets have suffered from a variety of defects which inhibit advantageous operation in a number of lifting applications. For example, the provision of a single specific lifting surface as opposed to a lifting surface disposed over the entire surface area of the electromagnet, limits the amount of material that can be lifted, particularly where the lifting material is a loose fill material such as pellets or the like. In addition, it is oftentimes difficult to position the lifting surface squarely against the item to be lifted in order to take advantage of the narrowly directed flux lines emanating from the lifting surface. Such a problem obviously complicates operation in environments such as a scrap yard where a wide variety of shapes and dimensions occur on the items to be lifted, or where the items are entangled or covered.
Another problem with electromagnets utilizing a lifting surface in magnetic communication with a core within the electrical coil is the frequency of mechanical damage to the core and lifting surface plate with repeated shock and harsh engaging action to the specific lifting surface of the magnet. Where such mechanical damage occurs to the core or lifting surface, moisture frequently has access to the electrical coil which damages the coil and adversely effects the operation of the magnet.
The present invention contemplates a new and improved electromagnetic lifting device which overcomes all the above referred to problems and others to provide a new lifting electromagnet which is simple in design, economical to manufacture, readily adaptable to a plurality of lifting uses with magnetic items having a variety of dimensional characteristics, provides a 360.degree. magnetic flux pattern for attracting items over the entire surface area of the device, and provides improved insulation and protection of the coil from operational hazards.